A spectrophotometric and first derivative spectrophotometric determination of iron(III) is carried out with 1-nitroso-2-naphthol as complexing reagents in aqueous phase using non-ionic surfactant. Tween 40. The iron is determined in the range 1.7-120 ng mL-1 with detection limit (2α) of 1.7 ng mL-1. The molar absorptivity and sandell’s sensitivity are 1.69 x (104 mol-1 cm-1) and 7.9 ng cm-2 at 446c nm. The optimum pH of the complex is 1. The critical micelle concentration (cmc) of Tween 40 is 5%. Absorption maximum of the complex for higher sensitivity and to overcome interference due to presence of certain metals ions. The presents method is compared with that of AAS and no significant difference is noted between the two methods at 95% confidence level. The method has been applied has been applied for the determination of Fe(III) in industrial waste water and steel samples.